The project is concerned with measurement of cyclic 3', 5' guanosine monophosphate in the epithelial cells of the toad urinary bladder and an examination of changes in the cyclic 3', 5' guanosine monophosphate content elicited by agents that affect transport and permeability properties of the bladder. A second phase of the study is devoted to characterizing cyclic nucleotide phosphodiesterase activity in the bladder and the effect of aldosterone on the enzyme.